X-ray tube with cooling jacket for target



M. E..WEISS 3,358,168

X-RAY T BE WITH COOLING JACKET FOR TARGET v 2 Sheets-Sheet 1 Filed Jan 6, 1965 wwwsw'ron. MOQTIMER E: His/$5 BY fi/ i flr ramvsys.

Dec. 12, 1967 M. E. wElss 3,358,168

X-RAY TUBE WITH COOLING JACKET FOR TARGET Fild Jan. 6, 1965 2 Sheets-Sheet 2 f V JNVENTQR;

i 1 V MOQT/MEQ Ea/$5 r r BY o Q WM z W flrrazusys.

United States Patent 3,358,168 X-RAY TUBE WITH COOLING JACKET FQR TARGET Mortimer E. Weiss, Santa Monica, Calif., assignor to Morris Associates, Hawthorne, Calif, a partnership Filed Jan. 6, 1965, Scr. No. 423,685 8 Claims. (Cl. 31336) This invention relates generally to X-ray tubes, and more particularly concerns significant improvements in the construction thereof resulting in several advantages including marked reduction in overall tube size.

In the past X-ray tubes have generally been constructed to have glass envelopes containing the electron beam directing means. Disadvantages include limitations preventing reductions in tube size since the glass must be spaced sufficiently from high voltage electrodes to resist puncture during arcing. Other disadvantages with glass envelopes include undesirable sensitivity to mechanical and thermal shocks.

It is a major object of the invention to overcome the above disadvantages as well as others associated with conventional X-ray tubes, through the provision of a tube of particularly advantageous design and construction, and wherein the tube length and diameter may be substantially less than are necessary to maintain in conventional high voltage tubes. Basically, the novel X-ray tube comprises an upright tubular body having an X-ray passing side port, first means to be supplied with high voltage for directing a beam of electrons to travel generally lengthwise within the body, a target located within the body to receive impingement of the beam and to direct an X-ray beam through the side port, a ceramic envelope about the electron beam directing means to protect against high voltage arcing, and a base integral with the envelope to support the electron beam directing means within and spaced from the envelope with the base spaced from the body. By this particular manner of utilization of a ceramic envelope, which for example may have twice the dielectric voltage breakdown strength of glass, the size of the tube can be materially reduced for the same high operating voltages as for example 100,000 volts. Further, the ceramic envelope offers virtually puncture proof protection against high voltage arcing, inasmuch as the melting point of the ceramic material may be several times that of glass. Also, because of the higher melting point and dimensional stability of the envelope under high temperature, it becomes possible to outgas the tube under more rigorous processing conditions, yielding more reliable operation and in creased life, the tube envelope being much more resistant than glass to mechanical and thermal shocks.

Other objects and advantages of the invention include the provision of a ceramic envelope tube wherein the base has a flange that is an integral part of the envelope to expand and contract therewith, and contributing to foreshortening of the tube overall length; the provision of a getter carried by the base to be flashed in response to current flow, together with a shield carried by the base to extend between the getter and the ceramic envelope for blocking flashing of the getter on the envelope; the provision for evacuation-pumping the tube through the anode and target support insert, with the latter including a portion subject to rapid sealing off immediately following evacuation; the provision for water cooling the anode in closely spaced relation to the target; the provision of novel and efficient electrical terminal structure and associated elements carried by the base, as well as a plug and shell structure to contain an insulative gas about the plug and envelope.

These and other objects and advantages of the invention, as well as the details of an illustrative embodiment,

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will be more fully understood from the following detailed description of the drawings, in which:

FIG. 1 is a vertical section taken through the overall assembly;

FIG. 2 is a vertical section taken through the upper part of the X-ray tube during outgassing thereof;

FIG. 3 is an enlarged vertical section showing the base, getter and terminal structure associated therewith;

FIG. 4 is a perspective showing of a portion of the getter; and

FIGS. 5, 6 and 7 illustrate modifications of the assembly.

Referring to FIG. 1, the illustrated X-ray tube includes an upright generally tubular anode body such as is seen at 10, and typically having a tubular outer section 11 and a tubular insert 12 carried by the outer section. Insert 12 fits in the bore 13 of the outer section 11 and is spaced inwardly of the counterbore 14 to provide a water circulation passage 15 extending in quite close cooling relation to the target 16 carried by the insert. I

The insert forms an outgassing passage 17 communicating through the outer section with the interior 18 of the tube, and particularly a ceramic envelope 19, whereby the X-ray tube may be rapidly evacuated by removing gas or air upwardly through the passage 17. The insert also includes a seal at the upper terminal of the passage 17, which is formed in an unusually efi'icient manner by crimping at 22 a stub tube 20 carried by the insert, and immediately following the outgassing or pumping operation. The latter is better illustrated in FIG. 2, with a suction duct 21 attached to stub tube 20. Following the outgassing step and crimping of the tube 20, a cap 23 is attached to the outer section 11 to provide inlet and outlet ports 24 and 25 for circulating coolant fluid such as water through the passage 15 and about the insert, the water being kept out of the tube interior by crimping 22.

The body 10 has a side port 26 typically closed by a beryllium window or plate 27 characterized as passing X-rays, the latter being generated at the target 16 in response to impingement thereon of a beam of electrons. Means supplied with high voltage for directing such a beam of electrons at the target may include the cathode or filament structure 28 carried within a focus cup 29 spaced from a focus hole 30 in the lower portion of the anode body 10. Accordingly, the electron beam is focused to travel generally lengthwise within the body 10 and toward the target 16.

A dielectric ceramic envelope 19 extends about the filament 28 and cup 29, as well as other components carried by base structure 31 to protect against high voltage arcing, and base structure 31 is made integral with the envelope to support said components within and spaced from the envelope with the base spaced from body 10. Also, the base and envelope 19 act to hold the vacuum in the interior zone 18. A particularly advantageous and unusual construction of the base, as illustrated, affords considerable foreshortening of the overall tube length. Thus, the base includes a first annular metallic flange 32 having sealing attachment with the envelope at 33, that flange and envelope having substantially the same coeflicient of thermal expansion. In this regard, the envelope composition may consist of 98-99% A1 0 the balance consisting of SiO and the flange 32 may comp-rise Kovar metal. Flange 32 may be hermetically joined to the envelope as by brazing to a metallized band baked onto the ceramic. Such metallizing processes are known in the art, the band material containing molybdenum and manganese and being painted onto the ceramic prior to baking.

The base also has electrical terminal structure including a second annular metallic flange 34, typically consisting of Kovar, and having hermetic sealing attachment to the first flange at 35. The terminal structure also includes a contact such as is seen at 36 carried by the second flange 34 and inwardly thereof, as for example by the outer dielectric ceramic ring 37 hermetically sealed to flange 34, the Kovar mounting plate 38 sealed to the ring 37, and the inner dielectric ceramic ring 39 hermetically sealed to and suspended from plate 38 and also suspending the contact 36. An electrically conductive post 91 carried by the contact 36 mounts one end of the filament 28. The opposite end of the filament is connected at 46a to conductive post 46. A getter tube 40 containing getter 41 exposed at the inner side of the tube 40, is connected between the outer flange 34 and the mounting plate 38 as by structure 40a and 40b.

When a high electrical current is applied between plate 38 and flange 34 as by terminal 43 and probe contact 55, the getter 41, typically comprising barium, is heated and flashed to combine with any remanent gas in the X-ray tube thereby forming stable chemical compounds of barium. Note in this regard that the getter may be flashed independently of the filament. Thus, the tube internal pressure may be dropped to as low as 10 mm. of Hg. Flashing is directed inwardly and away from the nearest portion of the envelope 19 to prevent high voltage arcing thereagainst. In addition, a protective skirt or shield 45 is carried by the base 31, and typically is suspended from cup 29, to extend between the getter and the ceramic envelope to block flashing of the getter on the envelope. Posts 46 support the cup 29, and are mounted on plate 38. FIG. 3 shows plug terminals 42 and 43 respectively engaging contact 36 and second flange 34.

Finally, an outer shell structure 47 contains the electrical current supply plug 50 and envelope 19, and extends in sealing relation therewith at spaced locations 51 and 52. Typically, O-rings 53 and 54 seal oflF between the structure, as for example between the envelope and the shell, and between the plug and the shell. The shell contains a dielectric insulating fluid about the envelope and plug. Insulating gases such as sulfur hexafluoride (SF or octofluorocyclobutane (C F may be used.

The envelope 19 is seen to be integrally connected to the body 10 as by the Kovar flanged bracket braze connected to a metallized band on the ceramic in the same manner as described above. Retaining cap 61 is fastened by screws 62 to the top plate 51 welded to shell structure 47, and seals the tube by compressing the O ring 53 in its groove.

In FIG. 5 the illustrated modified ceramic envelope is generally cylindrical and has a central axis 71. The outer surface 72 of the envelope intersects axial radial planes along convoluted paths, as indicated, said paths generally have ripple configuration. Thus, the surface 72 presents much greater area to the dielectric gas or liquid outwardly of the envelope and within shell structure 73, whereby the risk of arcing is correspondingly substantially reduced.

In FIG. 6 the dielectric ceramic envelope 75 extends about the filament 76 and cup 77, as well as other components carried by base structure 78 to protect against high voltage arcing, and again the base structure is made integral with the envelope to support the components within and spaced from the envelope. Base 78 and envelope 75 act to hold the vacuum in the interior zone 79. Foreshortening of tube length results from the base construction, including a first annular metallic flange 84) having sealing attachment with the envelope at 81, in a manner similar to attachment 33 in FIG. 1.

Electrical terminal structure provided by the base includes a second annular metallic flange 82 hermetically attached to flange 80. The terminal structure also includes a contact such as is seen at 83 carried by the second flange 82, as for example by the dielectric ceramic ring 84 hermetically sealed to flange 82 at 85, and to the contact at 86, generally inwardly of flange 80. Flanges and 82 and contact 83 may be made of Kovar. An electrically conductive post 87 carried by contact 83 mounts one .end

of the filament 76, the opposite end of the latter being connected to a cup supporting post 88 which return current to flange 82 at 82a. Current may be supplied via plug terminals 89 and 90 engageable with contact 83 and flange 82.

The getter in this form of the invention is retained in a tube 91 making electrical contact with flange 82 and with other electrical terminal structure 92, thereby to pass current to flash the getter for reducing the gas pressure in the tube below that established by pumping air from the tube. Said other terminal structure 92 is spaced from the base and carried by the envelope to be exposed at the exterior thereof for contact with an exterior power supply probe 93. Structure 92 may comprise a metallic ring hermetically sealed to the envelope 75 at its upper and lower annular faces. Thus the getter may be flashed independently of energization of the filament 76.

Finally, FIG. 7 illustrates a modified ceramic envelope 95 which is axially tapered, and closely received within a solid dielectric receptacle 96 having a tapered bore 97. Receptacle 96 may comprise rubber, and an air tight seal may be established with the tube and envelope by initially applying a dielectric lubricant coating to the receptacle inner surface or to the envelope outer surface, i.e. prior to assembly. Outer shell structure 98 contains the receptacle and envelope, as well as a current supply plug 99, the tube base and terminal structure remaining the same as for example is seen in FIG. 6. As a result, the tube may be changed in a manner of minutes, rather than hours as in the past, where it is necessary to pump down the space within structure 98 and to introduce a dielectric fluid therein whenever the tube is changed. The lubricant coating may comprise grease.

I claim:

1. In an X-ray tube, the combination comprising,

an upright high voltage insulative ceramic tubular envelope,

a base closing the ceramic envelope at the lower end thereof and carried by the envelope,

a cathode carried by said base interiorly of and spaced from the envelope for directing a beam of electrons to travel generally upwardly from within said envelope,

means closing the ceramic envelope at the upper end thereof and including an upright tubular body having a side window spaced above the level of said ceramic tube, the body having a bore and counterbore in vertical alignment with said cathode, the counterbore being located above the level of said window,

said means including an insert received downwardly into the body bore to project in said counterbore, the insert forming an outgassing passage communicating through the body lower portion with the interior of the ceramic envelope,

a target on said insert within the body to receive impingement of said beam entering said body and to direct an X-ray beam through said window,

said means also including a seal at the upper terminal of said outgassing passage,

and a closure carried by the upper terminal of said body to confine coolant circulating in said counterbore and about said seal in cooling relation with the insert and said body.

2. The combination of claim 1 including a getter carried by said base, the base having electrical terminal structure for passing electrical current to flash the getter thereby to reduce the air pressure in the tube below that established by pumping air from the tube, and a shield carried by said base to extend between the getter and the ceramic envelope to block flashing of the getter on said envelope.

3. The combination of claim 2 in which the base includes a first annular metallic flange having sealing attachment with said envelope, said flange and envelope having substantially the same thermal coefiicient of expansion, said terminal structure including a second annular metallic flange having sealing attachment to said first flange.

4. The combination of claim 3, including a cup carried by said second flange and located for focussing said beam of electrons toward said target, and said terminal structure includes a contact carried by said second flange and spaced inwardly thereof to receive engagement of a plug terminal when the second flange is engaged by another terminal of the plug.

5. The combination of claim 4 including a plug providing said terminals in engagement with said second flange and contact, the plug extending generally coaxially with said envelope, and an outer shell structure containing said plug and envelope and extending in sealing relation therewith to contain a dielectric insulating fluid about the envelope and plug.

6. The combination of claim 1 including a getter within said envelope, the base having certain electrical terminal structure, there being other electrical terminals spaced from the base and carried by said envelope to be exposed at the exterior thereof, and an electrical connection extending within the envelope and between said certain and other electrical terminal structure to pass electrical current to flash the getter thereby to reduce 6 the air pressure in the tube below that established by pumping air from the tube.

7. The combination of claim 1 in which said ceramic envelope is axially tapered, and including a high dielectric receptacle having a tapered bore closely receiving said tapered envelope.

8. The combination of claim 7 including an outer shell structure containing said receptacle and envelope, and a current supply plug having a terminal in electrical communication with said first means via the base, said outer shell structure extending about the plug.

References Cited UNITED STATES PATENTS 2,168,780 8/1939 Olshevsky 313330 X 2,332,426 10/1943 Atlee 313174 X 2,453,798 11/ 1948 Kloos 313-32 X 2,667,593 1/1954 Doolittle 313-7 X 2,679,017 5/ 1954 Rogers et a1 313249 X 2,708,250 5/1955 Day 313-249 X 2,749,527 6/1956 Gast 3 133 18 X 2,814,750 11/1957 Polese 313-246 X 2,836,748 5/1958 Atlee 31355 X 2 DAVID J. GALVIN, Primary Examiner. 

1. IN AN X-RAY TUBE, THE COMBINATION COMPRISING, AN UPRIGHT HIGH VOLTAGE INSULATIVE CERAMIC TUBULAR ENVELOPE, A BASE CLOSING THE CERAMIC ENVELOPE AT THE LOWER END THEREOF AND CARRIED BY THE ENVELOPE, A CATHODE CARRIED BY SAID BASE INTERIORLY OF AND SPACED FROM THE ENVELOPE FOR DIRECTING A BEAM OF ELECTRONS TO TRAVEL GENERALLY UPWARDLY FROM WITHIN SAID ENVELOPE, MEANS CLOSING THE CERAMIC ENVELOPE AT THE UPPER END THEREOF AND INCLUDING AN UPRIGHT TUBULAR BODY HAVING A SIDE WINDOW SPACED ABOVE THE LEVEL OF SAID CERAMIC TUBE, THE BODY HAVING A BORE AND COUNTERBORE IN VERTICAL ALIGNMENT WITH SAID CATHODE, THE COUNTERBORE BEING LOCATED ABOVE THE LEVEL OF SAID WINDOW, 